The present invention relates generally to fiber-optic communications systems and more particularly, concerns an apparatus and method for ensuring continuity of communications upon the failure of a fiber-optic link.
Fiber-optic communications is gaining popularity, and an increasing number of locations are now able to enjoy the benefits of such communications. Increasingly, fiber-optic links are being provided from a central office to a customer's property. In some instances, a direct fiber is provided between a central office and the customer, but more often, each fiber leaving the central office is shared by many customers. This can be done through an active optical network (AON) or a passive optical network (PON). In an AON, the central office and the customers are connected through a network via active components, typically an Ethernet network, and in a PON communications downstream from the central office to the customers are provided via an optical splitter with encryption while upstream communications from customers are combined using a multiple access protocol, such as time division multiple access (TDMA). For example, the FiOS fiber-optic network service available from Verizon Communications utilizes a PON.
Thus, at least for certain optical links, there is a need for transmitting timing for TDMA, encryption keys, power level, error correction codes and signals associated with networking. When a fiber optic link at the central office fails, it is a common practice to simply replace the link by switching over to a new fiber-optic link. During the replacement, communications are interrupted. When the link is replaced, the system goes through an adaptation phase during which all the communication equipment adjusts to the new link. Then, there is also a delay as various electronic interactions take place to restore synchronization, timing, error correction and proper encryption. As the signals traverse through plural network elements, the delay is accumulated and gets worse.
Upon failure of an optical link, it would be desirable to provide a graceful switchover to an operational optical link, so as to minimize and, preferably eliminate, loss of continuity of communications.